1. Field of the Invention
The present invention relates to a solid-state image sensing device and a manufacturing method thereof. Specifically, the present invention relates to a solid-state image sensing device and a manufacturing method thereof in which miniaturization of device does not deteriorate image properties.
2. Description of the Prior Art
In recent years, among solid-state image sensing devices, a solid-state image sensing device using an amplification-type MOS sensor has been a subject of interest. In this solid-state image sensing device, a signal detected by a photodiode is amplified by a transistor on a pixel to pixel basis. Such solid-state image sensing device is characterized by high sensibility. Moreover, due to miniaturization of pixels in recent years, a device isolation structure formed by Shallow Trench Isolation (STI) is employed for solid-state image sensing devices. STI is the technique of forming a trench on a principal surface of a semiconductor substrate, forming a dielectric film, such as oxide film, in the trench, and performing planarization, so that a device isolation region is formed. Side surfaces of the trench can be formed by STI at a steep angle to the principal surface of the semiconductor substrate. Therefore, the width of the device isolation region formed by STI is narrower than that of a device isolation region formed by LOCOS (Local Oxidation of Silicon).
However, progressing miniaturization of device requires a high impurity concentration and a deep diffusion region of the photodiode in order to improve saturation characteristics of the solid-state image sensing device. However, an incident light at an oblique angle to the deep diffusion region may produce charges in a deep portion of the photodiode, and the generated charges may be stored as signal charges in an adjacent photodiode, which may cause a problem, so-called cross talk.
A method to solve the above-mentioned problem, that is, the cross talk due to a deep photodiode, is disclosed in Gazette of Japanese Laid-Open Patent Publication No. 2003-142674 (patent document). Referring to FIG. 16, a solid-state image sensing device disclosed in the document will be described below.
As shown in FIG. 16, a P-type silicon substrate 101 has a trench isolation region 102 which isolates a pixel region. The pixel region has a charge storage portion (photodiode) 103 formed by an N-type impurity layer, a transfer gate 104 for transferring charges stored in the charge storage portion 103, and a floating diffusion (FD) portion 105 for storing the transferred charges.
In this case, a P-type device isolation diffusion region 106 surrounds the trench isolation region 102. The P-type device isolation diffusion region 106 extends under a bottom surface of the trench isolation region 102 to a position deeper than the charge storage portion 103. This structure allows to block a transfer of charges between pixels and thus to prevent the cross talk even in a case of a deep charge storage portion 103 due to the progressing miniaturization of device.